AlexZhukovich / CompareVerifier

CompareVerifier is a Java unit tests tool to verify Comparator and Comparable implementation correctness

CompareVerifier

CompareVerifier is a pure Java library that can be used in Junit tests to verify that classes implementing Comparable interfaces are defined correctly.

By default verification includes:

• compareTo being consistent with equals
• compareTo failing on a null argument
• satisfying sgn(a.compareTo(b)) == -sgn(b.compareTo(a))
• satisfying sgn(a.compareTo(c)) == sgn(b.compareTo(c)) => sgn(a.compareTo(b)) == 0
• satisfying sgn(a.compareTo(b)) > 0 && sgn(b.compareTo(c)) > 0 => sgn(a.compareTo(c)) > 0

Usage

    final VerificationInstancesCreator<BigDecimal> lesserCreator =
            VerificationInstancesCreators.from(
                new BigDecimal("0.0"), // smaller then the objects returned by
                new BigDecimal("1.0"), // both equal creator and greater creator
                new BigDecimal("2.0")
            );
    final VerificationInstancesCreator<BigDecimal> equalCreator =
            VerificationInstancesCreators.from(
                new BigDecimal("42.0"),
                new BigDecimal("42.0")
            );
    final VerificationInstancesCreator<BigDecimal> greaterCreator =
            VerificationInstancesCreators.from(
                new BigDecimal("101.0"), // larger then the objects returned by
                new BigDecimal("202.0"), // both equal creator and lesser creator
                new BigDecimal("303.0")
	    );
    
    ComparableVerifier
        .<Foo>forInstances(lesserCreator, equalCreator, greaterCreator)
	.verify();    

Where:

• lessInstancesCreator creates instance of the class implementing Comparable that are less then instances created by equalInstancesCreator
• equalInstancesCreator creates instances that should be equal to each other, they should be greater then those created by lessInstancesCreator and less then those created by greaterInstancesCreator
• greaterInstancesCreator creates instances that should be greater then those created by the two other creators

It's possible to disable one or more of the default verification checks by using set of "suppress" methods.

    ComparableVerifier
        .<Foo>forInstances(lesserCreator, equalCreator, greaterCreator)
        .suppressConsistentWithEquals(true)
        .suppressExceptionOnCompareToNull(true)
        .verify(); 

Download

You can use this library in conjunction with JUnit 4.12. There are two ways of getting the library:

• through releases
• through the use of JITPACK.io

To configure your project with JITPACK you need to in your build.gradle file at the end of repositories section add this line:

	allprojects {
		repositories {
			...
			maven { url 'https://jitpack.io' }
		}
	}

Add ComparatorVerifier to the list of your test dependencies:

	dependencies {
	        testImplementation 'com.github.foobaz42:CompareVerifier:master-SNAPSHOT'
	}

TODO

There are several missing things:

• transitivity checks
• other suppress options
• detailed usage examples
• CI